Polyurethane foams are used for a wide variety of applications, such as thermal insulation, packaging, upholstery, carpet underlay, automobile dashboards and structural material. An important factor to be considered in employing polyurethane or other polymeric foams is the ability of such foams to resist ignition, or once ignited, to be self-extinguishing after the ignition source is removed. This factor becomes even more important if the foam is to be used within a confined space.
As those skilled in the art are aware, the most common method of decreasing the flammability of polyurethane foams is by incorporating a flame retarding agent, such as a halogen- or phosphorus-containing compound, into the foam formulation. Although such compounds provide some improvement in the flame retardation properties, relatively large quantities of these agents may have to be employed to obtain satisfactory results.
For many years, the dominant blowing agents used to expand polyurethane foam had been the cholorfluorocarbons. These blowing agents were phased out after having been determined to pose a threat to stratospheric ozone. After the cholorfluorocarbons were phased out, the most common class of blowing agents became the hydrogenated chlorofluorocarbons. Although these are considered to be somewhat more environmentally friendly expansion agents, the hydrogenated chlorofluorocarbons still contain some chlorine. The chlorine atoms of hydrogenated chlorofluorocarbons are stable at altitudes under the stratosphere, and thus have a lower ozone-depleting potential (“ODP”). However, because of the hydrogenated chlorofluorocarbons still have a small ODP, they have also been mandated for eventual phase out. Water and/or carbon dioxide are rapidly becoming the blowing agents of choice for polyurethane foam manufacturers.
As known to those skilled in the art, polyurethane foams can be made using trimethylolpropane-based polyols (See e.g., U.S. Pat. Nos. 6,319,962, 4,690,954 and 4,407,981). Although there are some polyurethane foams available that pass the ASTM E-84 Tunnel Test “Standard Test Method for Surface Burning Characteristics of Building Materials” (ASTM International) with a Class I rating (U.S. Pat. Nos. 4,797,428 and 4,940,632), these foams use the alternative chlorofluorocarbon/hydrogenated chlorofluorocarbon blowing agents in combination with highly loaded polyester polyol blends and liquid flame retardants or have high flame retardant filler loadings, including phosphorus-based materials, in combination with trimethylolpropane-based polyols to produce the desired end result. These polyester-containing foams tend to reduce long term hydrolytic and “creep” stability and thus become a problem for applications outside of insulation-type foams.
Therefore, despite the abundance of disclosed processes to obtain flame retardant foams, polyurethane foam manufacturers remain interested in a foam that is solely water-, or carbon dioxide-blown; that satisfies the tunnel test of ASTM E-84 with a Class I rating; and that is free from trimethylolpropane-based polyols with phosphorus-based flame retardants.
Development of such a flame retardant polyurethane foam would therefore be very desirable. Furthermore, because of environmental concerns, it would be further desirable that such a foam use non chlorofluorocarbon/hydrogenated chlorofluorocarbon-containing blowing agents, such as water and/or carbon dioxide.